A gas with a surprisingly big job

Nitric oxide (NO) is a tiny molecule made of one nitrogen atom and one oxygen atom. For a long time it was thought of mainly as an air pollutant. Then researchers found that the body makes it on purpose, and that it acts as a messenger telling blood vessels when to relax. The discovery earned a Nobel Prize in 1998 and changed how scientists think about circulation.

The thin layer of cells lining every blood vessel, called the endothelium, releases small amounts of NO all day. The gas drifts into the muscle wall of the vessel and switches on a signaling chain (through a molecule called cGMP) that lets the muscle loosen. The vessel widens, which is called vasodilation, and more blood can flow through.

Why circulation and intimacy are linked

Arousal is, in large part, a circulation event. In men, erectile tissue fills with blood when the arteries supplying it relax. In women, the clitoris and surrounding tissues swell in a similar way, and blood flow supports natural lubrication. In both cases, nitric oxide released by nerves and vessel linings is a key trigger.

This is also why sexual changes can be an early signal of wider vascular health. The factors that stiffen arteries and damage the endothelium over time, such as smoking, high blood pressure, diabetes, high cholesterol and inactivity, tend to reduce NO availability as well.

From amino acid to open vessel

The body builds nitric oxide from L-arginine, an amino acid found in protein-rich foods. An enzyme called nitric oxide synthase splits arginine to release NO, leaving behind another amino acid, L-citrulline. The kidneys can then turn citrulline back into arginine, so the two work as a loop.

The case for pairing citrulline with arginine

Taking arginine by mouth sounds like the obvious way to support this pathway, but much of it is broken down in the gut and liver before it reaches the bloodstream. Citrulline largely avoids that early breakdown. In a randomized, placebo-controlled crossover study in healthy volunteers, oral L-citrulline raised blood arginine levels more effectively than the same approach with arginine itself, and increased markers of NO signaling [1]. Using both together gives the body arginine directly and a steadier supply through citrulline.

Some formulas also add piperine, the compound that gives black pepper its bite. It is studied as an agent that can slow the breakdown of other nutrients. It can also change how some medicines are absorbed, which is one reason labels urge caution with other medications.

What the research shows, and what it does not

The evidence on these amino acids is encouraging in places and modest in others, so it pays to read it plainly.

  • Arginine and erectile function. A meta-analysis of randomized trials in men with mild to moderate erectile difficulty found that arginine supplements improved erectile function scores compared with placebo or no treatment, with mostly mild side effects [2].
  • A broader comparison. A 2024 network meta-analysis of nutraceuticals found that most showed no clear benefit; arginine was one of the few that appeared to be of some use, mostly in combination with prescription medicines [3].
  • Citrulline and blood flow. A review of citrulline studies in exercise found it reliably raises blood arginine and nitrate levels, but direct evidence of better blood flow after supplementation is still limited and inconsistent [4].

In short, there is a sound biological rationale and some supportive clinical data for the ingredients. That is not the same as proof that any particular product produces those results, and supplements are not a substitute for diagnosis or prescribed care.

Habits that support healthy blood flow

Whatever else you do, the basics carry the most weight for the endothelium:

  • Regular aerobic activity, which by itself encourages vessels to produce more NO
  • Meals rich in vegetables, legumes, nuts and whole grains
  • Not smoking, and keeping alcohol moderate
  • Keeping blood pressure, blood sugar and cholesterol in check
  • Enough sleep and some way to manage stress

Where Yrektal fits

Yrektal is a Health Canada licensed natural health product (NPN 80139622) from Veos Pharma. It features L-arginine, which supports the production of nitric oxide, a molecule involved in healthy vasodilation, to support male and female sexual health. Each capsule pairs L-arginine with L-citrulline and a small amount of piperine. Read the label in full before use and take it as directed.

When to talk to a health professional

Do not use Yrektal if you have had a heart attack. Speak with a health professional first if you have heart or kidney disease, follow a low-protein diet, are pregnant or breastfeeding, or take medicines for heart conditions, erectile dysfunction or blood thinning. Some people notice stomach upset. Because changes in sexual function can be an early sign of heart or blood-vessel disease, diabetes or hormonal shifts, they deserve a proper check-up rather than self-treatment alone. Seek urgent care for chest pain, shortness of breath or an erection lasting more than four hours.